The formation of dovetail and finger (or box) joints in woodworking by those in the woodworking trade or by the home-hobbyist normally involves tedious set-ups and mathematic procedures to assure properly sized and positioned wood cuts on each of the two (or more) workpieces to be cut and eventually joined together. Key to the formation of proper cuts is the need to precisely position each workpiece relative to the cutting tool such as a router bit or circular saw of standard or dado configuration. This alignment is normally accompanied by the use of a feed "fence" positioned along the tool work surface which allows an operator to feed a workpiece in abutment along the fence into the rotating tool for effecting a wood cut in the workpiece. In the case of dovetail and finger joints, both of equal or variable spacing, this has necessitated detailed calculations and alignment or measurement of the distance between the fence abutting surfaces and the desired position and width of the desired multiple parallel cuts in each workpiece. Since each workpiece in a joint are cut differently so as to be interfit with each other upon joint assembly, the fence must be adjusted for multiple different cuts on each workpiece, again lengthening and making more complicated the set-up time and effort for each cut. Obviously, this adds cost to the making of the joints for those making wood or plastic articles for sale.
A recent U.S. Pat. No. 4,793,604 discloses a jig for maintaining a workpiece in a predetermined position relative to a cutting tool which includes an end attached to the woodworking apparatus fence which jig allows precision movement of the fence in 1/32 inch (0.794 mm) intervals by movement of channels along a pair of toothed racks having teeth spaced at such intervals. The racks extend at right angles to the fence and includes a measuring scale to read the distance in inches and make measurements thereon from a bi-directional predetermined "zero" position. Portions of the jig can be moved along the racks and then locked in place to properly position the fence with respect to the cutting tool for a desired workpiece cut. In some applications two jigs are employed to position a workpiece in two axes. Incidental to the sale of the '60 patent jig termed an "INCRA JIG," an Owner's Manual is supplied which gives the actual measurements within 1/32 inch (0.0794 cm) for a variety of finger and dovetail joints which can be made utilizing the jig. The jig itself is clamped to the tool work surface and a moveable end of the jig attached to the fence. The clamp is knob-loosened and the one part of the jig attached to the fence moved along the parallel racks to a desired position as shown on the 1/32 inch scale exposed on the fixed part of the jig. The knob is then tightened and the fence is then in a position for the first cut. The procedure is repeated for each cut on a first workpiece and then repeated for each of the different cuts on a second workpiece, which workpieces will be later joined at the compatible cuts made in the respective workpieces.
An additional flat elongated slot is provided in the jig for an auxiliary metric scale for use in marking cuts in accord with metric metrology. The Owners Manual states also
"If you are using your INCRA JIG to make a series of cuts, such as dovetails, or a series of grooves or holes, it is often easier to first use a pencil mark to record all of the INCRA JIG settings for that series, before you start making your cuts. To do this, place a strip of masking tape in the auxiliary scale slot. Then with a pencil, place a mark on the tape at all of the INCRA JIG settings involved in the series. This enables you to quickly align your INCRA JIG on the pencil marks without having to remember the actual scale readings. The tape is easily replaced when you are ready to begin a different series of cuts."
This above jig is shown in part in FIG. 5 where jig 60 has one element 62 fixed in a C-clamp or the like (not shown) to a tool work surface 51 of a wood working tool 50 having a rotatable router bit 52 extending vertically therefrom. A pair of parallel racks 63 extend along the top surface of element 62. Similar interfitting racks (not shown) are provided on the underside of the other jig element 64 which is connected to fence 30. Knob 65 is loosened to move the element 64 tooth-by-tooth along element 62, to move the fence toward or away from the router bit so as to allow cutting of a workpiece 46 guided into the router bit while in abutment along the fence 30 to effect the desired cut groove in the workpiece. Slot 66 contains the measurement scale and slot 61 is the above described auxiliary slot.